The long term objectives of this research are to understand the molecular basis of ethanol-induced hypothyroidism, and to ultimately utilize this understanding to clarify the effects of ethanol on thermoregulatory function. Thyroid hormones are important regulators of body temperature. Accidental hypothermia is often finked to ethanol intoxication, and alcohol abuse or dependence is often linked to hypothyroidism. Alcohol-induced hypothermia in rodents has been widely used as a model system to study :he effects of acute and chronic ethanol; however, the central mechanisms whereby ethanol affects temperature regulation are poorly understood. Acute ethanol-induced hypothermia is associated with a potent suppression of thyroid activity, and the thyrotropic effect of acute cold exposure is blunted. However, cellular levels of mRNA encoding thyrotropin-releasing hormone (TRH) in neurons of the paraventricular nucleus .PVN) arc elevated by ethanol, and the cold-induced increase in TRH mRNA levels is completely blocked. Because TRH mRNA levels in the PVN are linked to TRH secretion, these findings strongly suggest that ethanol uncouples TRH biosynthesis from release mechanisms. The proposed studies are organized around the working hypothesis that ethanol inhibits TRH release, and that the resulting decline in thyroid hormones releases TRH expression from T3 negative feedback. Using both in vivo and in vitro approaches, these experiments will determine whether a) changes in pituitary sensitivity to TRH can fully account for the ethanol-induced decline in thyroid function, b) central administration of ethanol can produce the same effects on thyroid function and TRH gene expression, c) ethanol blocks the effect of cold on TRH expression by inhibiting afferents mediating the effects of cold, or by uncoupling TRH expression from trans-synaptic mechanisms. In each case, measurements will be made of thyroid hormones and thyrotropin (TSH) by radioimmunoassay in serum, TSH beta mRNA in pituitary by northern blots, and TRH mRNA in the PVN by in situ hybridization (ISH). ISH will be used so that vasopressin and beta-actin mRNAs can be measured in the same PVN as negative controls. These techniques will be linked to traditional neuroendocrine approaches including administration of drugs into the third ventricle, electrical stimulation of specific brain areas, and jugular cannulation. The working model also suggests a molecular mechanism of ethanol tolerance and withdrawal which will be tested by additional experiments. Understanding fundamental effects of ethanol on neural function related to body temperature control will not only lead to the possible development of a treatment for this syndrome, but will provide new insights into the central effects of ethanol in general and perhaps a molecular mechanism of ethanol tolerance.